The main components of a drivetrain of a motor vehicle are a drive assembly and a transmission. The transmission converts torques and rotation speeds, and transmits the traction force supplied by the drive assembly. The present invention concerns a method for operating a drivetrain that comprises at least a transmission and, as its drive assembly, a hybrid drive with an internal combustion engine and an electric motor.
In a drivetrain with a so-termed parallel hybrid drive, a clutch is positioned between the internal combustion engine and the electric motor of the hybrid drive, by means of which the internal combustion engine of the hybrid drive can be decoupled from drive output of the drivetrain. When such a drivetrain with a parallel hybrid drive is started up, typically the internal combustion engine is off and the clutch between it and the electric motor is disengaged. In such a case one also speaks of a purely electric-motor-powered start.
Then, when during starting a starting torque desired by the driver exceeds the maximum starting torque that can be furnished by the electric motor, the internal combustion engine has to be started. To do this, the clutch between the internal combustion engine and the electric motor must be at least partially engaged so that the combustion engine can be turned over and started by the electric motor.
Furthermore, it is then necessary to match the speed of the internal combustion engine to that of the electric motor and make a connection between them. This is made possible by appropriately controlling of the clutch between the internal combustion engine and the electric motor, and if needs be, by acting upon the motor itself.
Especially if, directly from when the vehicle is at rest, the driver desires a high starting torque, this procedure known from the prior art for starting a motor vehicle with a parallel hybrid drive can result in a relatively long delay before the internal combustion engine has been started up and is supplying torque to the drive output. This is perceived by the driver as disadvantageous. A method is therefore needed for operating a drivetrain with a parallel hybrid drive, in which even when the driver desires a high starting torque directly from when the vehicle is at rest, the internal combustion engine can be started up within the shortest possible time so as to supply the drive output with the starting torque desired.